The following patents were developed in a search in the Patent Office and provides a good disclosure of the types of similar devices known in the art: U.S. Pat. Nos.
868,058 2,985,242 891,038 3,191,685 2,324,170 3,223,171 2,417,265 3,550,687 2,538,485 3,837,406 2,555,461 3,848,676 56,791 -- Danish